1. Field of the Invention
Embodiments of the present invention relate to fuel vapor processing apparatus known as canisters that are mounted mainly to vehicles.
2. Description of the Related Art
JP-A-2005-195007 teaches a known fuel vapor processing apparatus that includes a case defining therein a gas passage. The case includes a charge port and a purge port that are disposed at one end of the gas passage for introduction of fuel vapor gas and for purging fuel vapor from the gas passage, respectively. The case further includes an atmospheric port disposed at the other end of the gas passage for introduction of air used for purging the fuel vapor. Three adsorption chambers are formed in the case along a direction of flow of gas through the gas passage. Adsorption material is filled into each of the adsorption chambers for adsorption of fuel vapor. Between each two of the three adsorption chambers positioned adjacent to each other in the direction of flow of gas through the gas passage, a spacing chamber is formed to connect between two adjacent adsorption chambers. The cross sectional flow areas of the two adjacent adsorption chambers and the spacing chamber are the same with each other.
As described above, in the known fuel vapor processing apparatus disclosed in JP-A-2005-195007, the cross sectional flow areas of two adjacent adsorption chambers and the spacing chamber are the same with each other. Therefore, the flow rate of air may not be changed during the flow of air through the two adjacent adsorption chambers. For this reason, if the flow rate of the air is high, it may be possible that fuel vapor cannot be sufficiently desorbed from the adsorption materials contained in the adsorption chambers, resulting in that the desorbing efficiency of fuel vapor may be lowered. If the fuel vapor remains in or on the adsorption materials without being desorbed, a problem may be caused that fuel vapor is blown toward the atmospheric port during filling of fuel or other occasion. Thus, the amount of fuel blown toward the atmospheric port (hereinafter called a “blow-through amount”) may increase as the amount of fuel remaining in or on the adsorption materials (hereinafter called a “residual amount”) increases.
Therefore, there has been a need in the art for a fuel vapor processing apparatus that can improve the fuel vapor desorption efficiency and can reduce the residual amount or the blow-through amount of fuel vapor.